1. Field of the Invention
The present invention relates to wireless communications, and more particularly, to coexistence with another time division duplex (TDD) system in a TDD-based wireless communication system.
2. Related Art
Wireless communication systems are widely spread all over the world to provide various types of communication services such as voice or data services. The wireless communication system is generally a multiple access system that can support communication with multiple users by sharing available radio resources (e.g., bandwidth, transmit power, etc.). Examples of the multiple access system include a code division multiple access (CDMA) system, a frequency division multiple access (FDMA) system, a time division multiple access (TDMA) system, an orthogonal frequency division multiple access (OFDMA) system, a single carrier frequency division multiple access (SC-FDMA) system, etc.
The institute of electrical and electronics engineers (IEEE) 802.16 standard provides a technique and protocol for supporting broadband wireless access. The standardization had been conducted since 1999 until the IEEE 802.16-2001 was approved in 2001. The IEEE 802.16-2001 is based on a physical layer of a single carrier (SC) called ‘WirelessMAN-SC’. The IEEE 802.16a standard was approved in 2003. In the IEEE 802.16a standard, ‘WirelessMAN-OFDM’ and ‘WirelessMAN-OFDMA’ are further added to the physical layer in addition to the ‘WirelessMAN-SC’. After completion of the IEEE 802.16a standard, the revised IEEE 802.16-2004 standard was approved in 2004. To correct bugs and errors of the IEEE 802.16-2004 standard, the IEEE 802.16-2004/Cor1 was completed in 2005 in a format of ‘corrigendum’. A standard based on the IEEE 802.16-2004/Cor1 is referred to as IEEE 802.16e or WiMAX.
In the IEEE 802.16 broadband wireless access working group, there is ongoing standardization effort for the IEEE 802.16m standard which is a new technical standard based on the IEEE 802.16e. The IEEE 802.16m standard requires flexible support for the conventional IEEE 802.16e standard as well as a new system. The IEEE 802.16m system is based on TDD. That is, uplink transmission and downlink transmission are achieved in the same frequency band at different times.
Deployment of various wireless communication systems results in a problem in coexistence between different systems. That is, the problem is that a plurality of systems provide services in the same region/time. In particular, in order for coexistence of the plurality of TDD systems, it is important to prevent uplink transmission and downlink transmission from being performed simultaneously. This is because a data loss may occur due to interference when downlink transmission and uplink transmission overlap between different TDD systems. In addition, symbol puncturing, time delay, or the like can be used to avoid interference, but this may cause a problem of decreasing spectral efficiency.